What is Suction Specific Speed and How can it be Used in Centrifugal Pump Selection?

A. Suction Specific Speed is an index that describes the characteristics of the suction side of the impeller. It is calculated using the NPSHr in feet, speed (N) in rpm, and flow rate (Q) in gpm at the pump’s Best Efficiency Point and maximum impeller diameter. The equation for Suction Specific Speed (designated Nss or S) is: